1. Field of the Invention
The present invention relates to a linear motor for giving thrust of free linear movement in one direction and a linear moving stage device capable of moving a stage by the provided linear motor.
2. Description of the Related Art
There are a movable magnet type and a movable coil type in a coreless linear motor of the related art. In the movable magnet type linear motor, coils have to be arranged on corresponding parts on the power supply side (primary side) over the almost all area of a movable stroke on the magnet side (secondary side). Therefore, the movable magnet type linear motor is liable to be an expensive device.
On the other hand, the movable coil type linear motor does not have such a disadvantage and is superior in that point.
As the movable coil type linear motor, those having a flat (approximately track shaped) coil as an armature fitted into a movable body attaching plate between magnets arranged to be facing to each other and arranged on both sides in the thickness direction of the movable body attaching plate are known (for example, Japanese Unexamined Patent Publication (Kokai) No. 2003-116262).
FIG. 10 is a view of the configuration of a coreless linear motor described in the patent publication, seen from a section perpendicular to a longitudinal direction (moving direction) thereof. FIG. 11 is a perspective view of a reinforcement member to be fixed to the movable body attaching plate and a coil to be fixed by being fitted in the reinforcement member.
The coreless linear motor 100 shown in FIG. 10 has a side yoke 101 having a recessed cross section, and permanent magnet series 104 and 105 are provided on facing surfaces of an upper piece (an upper side yoke 102) and a lower piece (a lower side yoke 103) of the side yoke 101. At this time, magnets composing the permanent magnet series 104 and 105 are lined up in the longitudinal direction (motor moving direction) of the side yoke 101, so that their magnetic polarities become opposite from that of adjacent magnet and the magnetic polarities of facing magnets on the upper side yoke side and the lower side yoke side become different. Between the facing permanent magnetic series 104 and 105, the movable body attaching plate 106 to be attached with a movable body on its open end side is inserted and reinforcement members 108 respectively mounted with coils 107 are fixed to the both sides in the thickness direction.
The reinforcement member 108 has an approximate flat shape as shown in FIG. 11 and composed of a nonmagnetic material, such as a resin. Annular grooves 108A to be almost fitted in with a shape of the hollow coils 107 are formed on one of the main surfaces (surface facing to the magnets) of the reinforcement member 108. On the reinforcement member 108 for a three-phase coil motor shown in FIG. 11, three annular grooves 108A are formed along the motor moving direction A and each of the hollow coils 107 is fitted in each of the annular grooves 108A. A raised part 108B corresponding to a coil bobbin is formed at an approximately center portion of the annular groove 108A in advance, and a hollow part 107A of the coil fits with the raised part 108B. As a result, each of the coils 107 after being mounted is in a state that much of the surfaces except for the magnetic facing surface are enclosed by a resin or other nonmagnetic material.
The reinforcement members 108 attached with the coils 107 are fixed to both sides in the thickness direction of the movable body attaching plate 106 and inserted to a space between facing magnets in the side yoke 101 as shown in FIG. 10. While not illustrated, the movable body attaching plate 106 at this time is supported to be linearly movable freely by the side yoke 101 or a not shown base for the side yoke 101 to be fixed to.
When a three-phase AC current flows to the three coils 107 as armatures, a Lorentz force due to magnetic strength and electric strength affects an assembled body, that is, the movable body attaching plate 106, coils 107 and reinforcement elements 108, as a movable unit for being attached with a movable body and generates thrust of a linear motor.
The movable coil type coreless linear motor can be variously used as a compact linear moving stage device to be incorporated, for example, in working machines and a variety of production apparatuses, etc. In that case, the device is demanded to be compact and to attain high control performance and low power consumption.
The coreless linear motor 100 having the configuration shown in FIG. 10, however, has disadvantages to be overcome explained below, for example, when being applied to a linear moving stage device.
In the linear motor configuration shown in FIG. 10, flat shaped coils 107 face to the permanent magnet series 104 and 105. The coils 107, the permanent magnet series 104 or 105, the upper side yoke 102 and the lower side yoke 103 compose a magnetic circuit. But it is difficult to attain a thin body with this configuration because of the points (1) to (4) below.
(1) As shown in FIG. 10, two coils 107 are arranged in the thickness direction, and each coil 107 has to face to the permanent magnetic series 104 or 105 by leaving a desired magnetic gap.
(2) When seeing the upper side yoke 102 and the lower side yoke 103 in the thickness direction, the yoke of a magnetic circuit has to be provided by the number of 2. The upper side yoke 102 and the lower side yoke 103 have to have a certain thickness so as not to cause magnetic saturation. Note that, even in the case where an affect by magnetic saturation is small and the yoke can be made thin to a certain extent, strong attractive forces of magnets act between the upper side yoke 102 and the lower side yoke 103 and there is a mechanical limit in the strength, so that the yokes have to have a certain thickness.
(3) In terms of mechanical strength, the movable body attaching plate 106 has to be also made thick to a certain extent.
(4) When placing a stage (not shown) at an upper position than the upper side yoke 102, an air gap has to be secured between the stage and the upper side yoke 102 because the upper side yoke 102 is fixed.
From the above points (1) to (4), the linear motor 100 itself configured as shown in FIG. 10 is thick, so that when it is applied to a linear moving stage device, there is a disadvantage that the linear moving stage device is hard to be made thin due to the configuration.
A bobbin of the coils 107 is made by a resin, etc. and much of the surfaces except for the magnet facing surface are enclosed by the reinforcement members 108 made by a resin, etc. as shown in FIG. 11, so that the thermal radiation characteristic is poor and an overheat state is liable to be caused when a current flows to the coils 107. Therefore, it is not possible to flow a large amount of current to the coils 107, consequently, the magnetic field has to be intensified, so that a thickness of the magnets composing the permanent magnet series 104 and 105 and a thickness of the yokes (the upper side yoke 102 and the lower side yoke 103), etc. tend to be thick.
A distance from a mounting portion of the coils 107 to a point of applying the thrust (that is, a stage position) is long and, moreover, the thrust is transmitted to the stage via the movable body attaching plate 106 having an L-shaped cross section, so that couple of forces to induce vibration particularly in the yawing direction is easily generated to hinder the performance of the stage. Therefore, a decline of a control gain is caused, and a decline of stability of a stage speed, a decline of a settlement time when aligning the stage, and a decline of holding accuracy become disadvantageous.